Chair with separate and interconnecting type lumbar and thoracic supports

ABSTRACT

The present invention relates to an apparatus for effectively purifying and neutralizing toxic gases such as odors, fumes or various volatile organic compounds generated by research laboratories, chemical processing factories or hospitals where medicinal products are handled. The apparatus according to the present invention comprises: a main body having an intake, an exhaust and a control panel; a pre-filter, a first filter, first and second neutralizing pellet beds, and a second filter which are mounted in the apparatus main body and are placed from the intake to the exhaust in that order; and a blower and a driving device placed between the first and second neutralizing pellet beds. The apparatus effectively purifies and neutralizes toxic gases and collects fine particles or dust. Thus, the apparatus helps to maintain health of researchers, people who perform experiments, workers in chemical factories, or medical workers, since the filter and neutralizing pellet bed are configured in a cartridge form, the apparatus is low-maintenance. Also, additional connection of other facilities or pipes is not required. Therefore, the apparatus has high usability due to the independent compact form and function thereof, and can be driven with less noise.

TECHNICAL FIELD

The present invention relates to a chair with separate and interconnecting type lumbar and thoracic supports. More particularly, the present invention relates to a chair with separate and interconnecting type lumbar and thoracic supports in that a back support is physically divided into a lumbar support and a thoracic support, the lumbar support is formed to be curvable, and the lumbar and thoracic supports are configured to be interconnected to each other, so that, when a sitter tilts his/her upper or lower back backward for rest or tension relief, the lower back area of the sitter is comfortably brought into contact with and supported by the lumbar support with a backward tilt of a relatively large angle, and at the same time, the upper back area of the sitter is comfortably brought into contact with and supported by the thoracic support with a backward tilt of a relatively small angle. Therefore, the lumbar and thoracic supports share the task of comfortably supporting the lumbar vertebra and thoracic vertebra respectively. In addition, the chair has high posture stability without falling backward when the sitter tilts his/her upper and lower back far backward.

BACKGROUND ART

Recently, in a fiercely competitive society, the use of computers has become part of man's life. Accordingly, a sedentary life of modern people in the chair has been remarkable increased in comparison with the past, and the peoples who complain of pain in the waist or spine, have been increased among students, test-takers, or office workers living a sedentary life in the chair for long periods of time.

These pains in the waist or spine are caused by a sitting of a continuous tension for hours, a habitually bad sitting posture, a sleep under a wrong posture and environment, or an applying of a big power in a wrong posture and so forth.

Accordingly, in the office chairs, in which a back support for supporting the lumbar and thoracic vertebra is integrally formed, it adopts an elastic structure capable of tilting most of the back support backward in some degree so as to ease the tension on muscles and ligaments for the lumbar and thoracic vertebra and take a rest from time to time during sitting for a long time.

However, in the conventional chair, in which the elastic back support for supporting the lumbar and thoracic vertebra is integrally formed, since the vertebration of a human body is bent in a S-shape from the side view thereof, when the sitter tilts his/her upper and lower back backward, the thoracic vertebrae is tightly supported by the upper half part of the back support, but the lumbar vertebra is separated from the lower half part of the back support owing to a big space between them, so that the lumbar vertebra is not supported by the back support. Since this phenomenon gets worse around the boundary between the lumbar vertebra and the thoracic vertebrae, there is a problem in that it is a major cause the boundary between the waist or waist part and the back is inversely strained or the sitter feels inconvenience.

Accordingly, in order to solve the above problem, an auxiliary cushion is used so as to fill the space between the sitter's back and the chair. However, since the body sizes and the postures of the sitters are difference from each other, it is not easy to select the proper auxiliary cushions in well with the volume, shape and elasticity thereof. Also, when the auxiliary cushions do not fit them properly, it has a marginal effect or on the contrary the posture thereof can become bad, or there is a fear of the loss thereof.

In order to solve the above-mentioned problems, as shown in FIG. 7, Korean Patent laying-open Gazette No. 10-2005-0046953 (laying-open date: May 19, 2005; Patent No. 10-0583585), which is filed by the present inventor, discloses a chair 1′ having a waist support in that a back support is divided into a back support 4 and a waist support 3, one end of a metal back support frame 4 a is connected to the back support 4, and an extending portion 4 e, which is other end of back support frame 4 a, is connected to a plate spring 4 f, which is extended to a multifunctional bracket 7 located on a lower portion of a seat 2. Also, as shown in FIG. 8, it has been disclosed a chair 1″ having a waist support in that a back support is divided into a back support 4, which is extended downward, and a waist support 3, one end of a plate spring 4 f is connected to the extending portion 4 e of the back support 4, and other end of the plate spring is connected to a multifunctional bracket 7 located on a lower portion of a seat 2. However, since the above-mentioned conventional chairs 1′ or 1″ have a stiffness that the waist support 3 integrally formed at the seat 2 is not tilted backward, the waist support is not interconnected to the back support 4. Also, because the back support is erectly and smoothly formed, when the sitter tilts the upper and lower back far backward, the gap is still generated between the lumbar vertebra and the back support, thereby it is ergonomically unsatisfactory in terms of comfortableness. Moreover, since the bending angle becomes larger in the boundary between the erected waist support 3 and the back support 4 tilted backward, still there is a problem in that it is a major cause the boundary between the waist or waist part and the back is inversely strained or the sitter feels inconvenience.

Also, because the metal back support frame 4 a of the conventional chairs 1′ or 1″ has a strip shape to be exposed to outside, there is a problem in that it lacks a sense of beauty in external appearance.

The reference numerals 6, 7 a, and 9 are an armrest, a frame, a supporting leg respectively.

DISCLOSURE Technical Problem

Therefore, the present invention has been made in view of the above-mentioned problems, and the primary object of the present invention is to provide an ergonomic chair with separate and interconnecting type lumbar and thoracic supports in that the lumbar vertebra and the thoracic vertebrae are clearly and tightly supported during sitting in a correct posture and they are tightly supported without generating a gap between the lumbar vertebra and the chair when a sitter tilts his/her upper and lower back far backward, thereby increasing the comfortableness.

A second object of the present invention is to provide an ergonomic chair with separate and interconnecting type lumbar and thoracic supports having an excellent posture stability of the chair itself as though a sitter tilts his/her upper and lower back far backward.

A third object of the present invention is to provide an ergonomic chair with separate and interconnecting type lumbar and thoracic supports in that, as though a sitter tilts his/her upper and lower back far backward, it can maintain as it stands without unfolding the sitter's arm placed on the armrest, thereby increasing in comfortableness and easefulness.

A fourth object of the present invention is to provide an ergonomic chair with separate and interconnecting type lumbar and thoracic supports in that the height of the armrest can be easily adjusted according to the height of the sitter and a use aspect thereof, thereby increasing in comfortableness and easefulness.

A fifth object of the present invention is to provide an ergonomic chair with separate and interconnecting type lumbar and thoracic supports in that a bending of a synthetic resin backing plate can be easily performed during bending of the thoracic vertebrae backward.

A sixth object of the present invention is to provide an ergonomic chair with separate and interconnecting type lumbar and thoracic supports capable of giving a good sense of seating to a seat.

Technical Solution

In accordance with an aspect of the present invention to achieve the first and second objects thereof, there is provided a chair with separate and interconnecting type lumbar and thoracic supports having a back support divided into a lumbar support and a thoracic support with a frame, a seat integrally formed on the lumbar support through an embedded frame, the frame of the thoracic support elastically and tiltably connected to another frame or a bracket located at a lower surface of the seat, and an armrest, wherein the embedded frame is divided into a main frame extending from the seat to a lower half portion of the lumbar support and at least one auxiliary frame located on an upper half portion of the lumbar support and a plate spring is attached backward over the main frame and the auxiliary frame, which are separated from each other.

In accordance with another aspect of the present invention to achieve the first and second objects thereof, there is provided a chair with separate and interconnecting type lumbar and thoracic supports, wherein the thoracic support comprises a short edge for contacting with an upper end portion of the lumbar support and an extending portion formed via the short edge.

In accordance with further another aspect of the present invention to achieve the third object thereof, there is provided a chair with separate and interconnecting type lumbar and thoracic supports, wherein one end of a frame of the armrest is fixed to a lower portion of an extending portion of the thoracic support through a fixing means, thereby the armrest is lifted by interlocking with the thoracic support during a backward tilting of the thoracic support.

In accordance with further another aspect of the present invention to achieve the fourth object thereof, there is provided a chair with separate and interconnecting type lumbar and thoracic supports, wherein the armrest comprises a height adjusting bracket having a plurality of fixing protrusions therein connected to the arm seat and a frame having one end portion thereof inserted into the height adjusting bracket and a plurality of grooves for inserting the fixing protrusions therein formed at said one end portion of the frame, and the height adjusting bracket is drawn from and out the frame by stages, thereby a height control of the arm seat or height and length control thereof can be simultaneously performed.

In accordance with further another aspect of the present invention to achieve the fifth object thereof, there is provided a chair with separate and interconnecting type lumbar and thoracic supports, wherein the thoracic support comprises a body, which is consist of a cushion material and a soft outer cover covering an outer surface of the cushion material, again the frame is fixed to a back surface of the body, a hard outer cover is covered and overlaid on a back surface of the frame, and a cutting portion is transversely formed at a position in that an extending portion of the hard outer cover is formed, whereby a bending stress can be released during backward tilting of the thoracic support.

In accordance with further another aspect of the present invention to achieve the sixth object thereof, there is provided a chair with separate and interconnecting type lumbar and thoracic supports, wherein at least one air entrance cap having a plurality of air inflow and outflow holes is formed at the side surface of the seat.

In accordance with further another aspect of the present invention to achieve the objects thereof, there is provided a chair with separate and interconnecting type lumbar and thoracic supports, wherein one end of a connecting frame is connected to a lower end portion of the frame of the thoracic support, other end of the connecting frame is inserted into and fixed to a pivotable frame of the bracket, which is pivotally mounted on the bracket fixed to a lower surface of the seat, by means of a link for controlling the length thereof, and the pivotable frame is elastically supported by a plate spring.

Advantageous Effects

The ergonomic chair with separate and interconnecting type lumbar and thoracic supports according to the present invention as described above has advantageous effects in that the back support is physically divided into the lumbar support and the thoracic support, the lumbar support is formed to be curvable, and the lumbar and thoracic supports are configured to be interconnected to each other, so that the lumbar vertebra and the thoracic vertebrae are clearly and tightly supported during sitting in a correct posture and they are tightly supported without generating a gap between the lumbar vertebra and the chair when the sitter tilts his/her upper and lower back far backward for rest or tension relief, thereby increasing in comfortableness and easefulness and having the excellent posture stability without overturning the chair, and selectively the height of the armrest can be easily adjusted according to the height of the sitter and a use aspect thereof, thereby more improving in comfortableness and easefulness and giving a good sense of seating to a seat.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view illustrating an erect status of a chair with separate and interconnecting type lumbar and thoracic supports according to one embodiment of the present invention;

FIG. 2 is a perspective view illustrating a backward tilting status of the chair of FIG. 1;

FIG. 3 is a side perspective view of FIG. 1;

FIG. 4 is a partially cut and longitudinally perspective view illustrating the erect status of FIG. 1;

FIG. 5 is a partially and longitudinally cut perspective view illustrating the backward tilting status of FIG. 2;

FIG. 6 is a side perspective view illustrating a chair with separate and interconnecting type lumbar and thoracic supports according to another embodiment of the present invention;

FIG. 7 is a partially cut and longitudinally perspective view illustrating an operating status of a conventional chair with separate type lumbar and thoracic supports; and

FIG. 8 is a partially cut and longitudinally perspective view illustrating an operating status of another conventional chair with separate type lumbar and thoracic supports.

BEST MODE Mode for Invention

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view illustrating an erect status of a chair with separate and interconnecting type lumbar and thoracic supports according to one embodiment of the present invention, FIG. 2 is a perspective view illustrating a backward tilting status of the chair of FIG. 1, FIG. 3 is a side perspective view of FIG. 1, and FIG. 4 and FIG. 5 are partially and longitudinally cut perspective views illustrating the erect status and the backward tilting status of FIG. 1 and FIG. 2 respectively. Here, the drawings are mentioned together for convenience.

The chair 1 with separate and interconnecting type lumbar and thoracic supports according to one embodiment of the present invention includes a seat 2, a backward bendable lumbar support 3 integrally connected to the seat 2, a thoracic support 4 with a frame 4 a physically separated from the lumbar support 3, a headrest 5 as an optional component, an armrest 6, a multifunctional bracket 7 for elastically supporting the thoracic support 4 and the lower portion of the seat 2 to be connected to each other, a central axis 8, and supporting legs 9 having casters 9 a.

Firstly, the seat 2 and the lumbar support 3, which are integrally formed each other, will be explained. It is equipped with a main frame 2 a of an approximate “L” shape formed inside an area extending from the seat 2 to a neighborhood of approximate lower half portion or center portion of the lumbar support 3 and an auxiliary frame 3 a formed inside an area extending from a neighborhood of approximate upper half portion or center portion of the lumbar support 3 to an upper portion of the lumbar support 3. A plate spring 3 b is attached backward over one end portion of the main frame 2 a extending to the inside of the lumbar support 3 and a lower end portion of the auxiliary frame 3 a, which are separated from each other, so that the lumbar support 3 is configured to be bent backward in a case that a force “A” is applied as shown in FIG. 2.

As though only one auxiliary frame 3 a an one plate spring 3 b is illustrated as the drawings, the present invention is not limited to the number thereof. If necessary, it can be configured to form a plurality of auxiliary frames and plate springs. More concretely, in a state that a plurality of auxiliary frame 3 a is separated from each other, each plate spring 3 b is attached backward in the intervals of both ends thereof, which are separated from each other, so that the lumbar support 3 can be gradually bent in phases.

As is generally known, the seat 2 and the lumbar support 3 includes the auxiliary frame 3 a and the main frame 2 a as a core, a conventional cushion material (no reference numeral) of surrounding them, and an outer cover (not shown) made of natural or artificial fibers, nonwoven fabrics, or artificial or natural leathers and covering the outer surface of the cushion material.

The lumbar support 3 includes a ring-shaped protrusion 3 c formed at a center of the front thereof considering a normal curvature of a human lumbar during erecting thereof. In this case, both sides of the ring-shaped protrusion 3 c are a relatively little more protruded, so that the central portion of the lumbar support 3 is softly surrounded, thereby it is desirable in terms of a decrease in fatigability.

In the meantime, if necessary, selectively, at least one conventional air entrance cap (not shown) having a plurality of air inflow and outflow holes is formed at the side surface of the seat 2, it can feel an air cushion during seating thereof. The install of the air entrance cap (not shown) is well-known in the art in a case that the outer cover (not shown) is sheets or leather of a synthetic resin.

Continuously, the thoracic support 4 is an independent member, which is separated from the lumbar support 3. The thoracic support 4 includes a short edge 4 d for contacting with an upper end portion 3 d of the lumbar support 3 and an extending portion 4 e via the short edge 4 d.

Also, the thoracic support 4 generally includes a frame 4 a as a core, a conventional cushion material (no reference numeral) of surrounding it, and an outer cover (not shown) made of natural or artificial fibers, nonwoven fabrics, or artificial or natural leathers and covering the outer surface of the cushion material. However, as shown in the drawings, considering economical and beautiful sight aspects, the thoracic support 4 includes a body which is consist of the cushion material (no reference numeral) and the soft outer cover (not shown) covering the outer surface of the cushion material. Also, the frame 4 a is fixed to a back surface of the body and again, a hard outer cover 4 b such as a synthetic resin board or a woody chip board etc. can be covered and overlaid on a back surface of the frame 4 a. In the latter case, if necessary, a cutting portion 4 g is transversely formed in a bending position of the hard outer cover 4 b, which is the starting area of the extending portion 4 e, so that the bending stress applied to the hard outer cover 4 b can be released during the backward tilting of the thoracic support 4.

A bending portion 4 c is formed at a center of the front of the thoracic support 4. At this time, both sides of the bending portion 4 c are also, a relatively little more protruded, so that the central portion thereof is softly surrounded over all, thereby it is desirable in terms of a decrease in fatigability.

The frame 4 a of the thoracic support 4 is extended to a lower end portion of the extending portion 4 e.

The headrest 5 is a choice, not a must in the present invention. It will be briefly described with reference to the accompanying drawings. However, the option and the difference in construction thereof can be changed arbitrarily according to the need.

As shown in drawings, a protrusion 5 a is formed at a front surface of the headrest 5. The back of the head can be comfortably covered and supported through the tension of the fabric and the weight applied to the lumbar vertebra and the thoracic vertebrae can be alleviated through the headrest 5. As shown, the headrest 5 is fixed to one end of the connecting frame 5 b through a connector 5 c and other end of the connecting frame 5 b can be directly connected to the upper end portion of the frame 4 a of the thoracic support 4. However, generally, the connecting frame capable of adjusting the height thereof is inserted into and fixed to the upper end portion of the thoracic support 4.

Next, the armrest 6 will be explained. The armrest includes arm seats 6 a for placing sitter's arm thereon, which is made of various materials such as a polyurethane etc. having good resilience and texture, and a frame 6 b for supporting it thereon. Generally, the frame 6 b is fixed to the following bracket 7 or other frame located on a lower surface of the seat 2. However, as shown, one end of the frame 6 b is directly fixed to a lower end portion of the frame 4 of the thoracic support 4 through a proper and arbitrary fixing means 6 c such as a fixing screw or a spot welding and so forth.

Accordingly, as shown in the drawings, one end of the armrest 6 is directly fixed to the lower end portion of the thoracic support 4, so that the armrest 6 is interconnected with the thoracic support 4 during the backward tilting of the thoracic support 4 in that a force “B” is applied as shown in FIG. 2, thereby the armrest 6 can be lifted. Therefore, when the thoracic support 4 is tilted backward, since it is unnecessary to again adjust the sitter's arm placed on the armrest 6, it can ease the tension and take a rest at ease and in comfort.

As though it is not shown in the corresponding drawings, similarly to another embodiment of the present invention of FIG. 6, a height adjusting bracket (for example, see the reference numeral 6 d of FIG. 6), in which a plurality of fixing protrusions (not shown) is formed, is integrally formed on the arm seat 6 a or connected thereto, a plurality of grooves (not shown) for inserting the fixing protrusion therein is formed at an insertion end portion of the frame 6 b, which is inserted into the height adjusting bracket, and the height adjusting bracket is drawn from and out the frame by stages, so that the height control of the arm seat 6 or the height and length control thereof can be simultaneously performed, which is also, within the scope of the present invention.

The bracket 7 as a multi-functional bracket is fixed to a lower surface of the seat 2. This part serves as a round lever for controlling the strength of the tension so as to control the strength of the tilting of the back support. That is, the bracket 7 includes a well-known rotation knob 7 b and a well-known angle control lever 7 c, which is applied to a synchronized tilting mechanism capable of performing the height control of the chair and the tilting angle control of the back support by stages and so forth.

A frame 7 a of the bracket 7 is pivotally mounted on one end of the bracket 7 by means of a link 7 e. Also, one end of a connecting frame 4 f is connected to the lower end portion of the frame 4 a of the thoracic support 4 and other end of the connecting frame 4 f is fixed to the frame 7 a of the bracket. The connecting frame 4 f is inserted into and fixed to the inside of the frame 7 a through a length control fixture 7 d for controlling the length thereof. Also, since the pivotable frame 7 a is elastically supported by the plate spring 7 f, during the backward tilting of the thoracic support 4 in that a force “B” is applied as shown in FIG. 2, the bracket 7 is slanted backward while it maintains the elastic dynamic stability thereof. On the contrary, if the backward tilting force is removed, it returns to the original condition for maintaining level.

In the meantime, selectively, in case of a swivel chair, the upper end portion of the central axis 8 is rotatably fixed to the bracket 7 and the lower end portion of the central axis 8 is rotatably inserted into the center of the supporting legs 9. The urethane casters 9 a can be mounted on the plurality of supporting end portions of the supporting legs 9, so that the concerns about the occurrence of a flow scratch and the noise are low, it is no fear of a damage thereof, and the durability is strong.

In the ergonomic chair 1 with separate and interconnecting type lumbar and thoracic supports according to the present invention having the above construction, when the sitter tilts his/her upper or lower back backward for rest or tension relief, the lower back area of the sitter is comfortably brought into contact with and supported by the lumbar support 3 with a backward tilt of a relatively large angle through the plate spring 3 b for backing the auxiliary frame 3 a, and at the same time, in a state that the short edge 4 d of the thoracic support 4 is contacted with the upper end portion 3 d of the lumbar support 3, the upper back area of the sitter is comfortably brought into contact with and supported by the thoracic support 4 with a backward tilt of a relatively small angle. Therefore, the lumbar and thoracic supports share the task of comfortably supporting the lumbar vertebra and thoracic vertebra respectively. In addition, the chair has high posture stability without falling backward when the sitter tilts his/her upper and lower back far backward, and also has an elegant look.

Especially, as shown in the drawings, during the backward tilting of the thoracic support 4, one end of the armrest 6 is connected and fixed to the lower end portion of the thoracic support 4, so that the arm seat 6 a of the armrest 6 is rotated together with the thoracic support 4, thereby it can be tilted and lifted upward. Therefore, since it is unnecessary to adjust the sitter's arm placed on the armrest 6, it can take a rest at ease and in comfort as it stands.

FIG. 6 is a side perspective view illustrating a chair 1 a with separate and interconnecting type lumbar and thoracic supports according to another embodiment of the present invention. Since the basic elements thereof are essentially the same as those of FIG. 1 through FIG. 5 except for the armrest 6, only the differences between them will be explained.

As shown, a height adjusting bracket 6 d, in which a plurality of fixing protrusions (not shown) is formed, is integrally formed on the arm seat 6 a, a plurality of grooves (not shown) for inserting the fixing protrusion therein is formed at an insertion end portion of the frame 6 b, which is inserted into the height adjusting bracket 6 d, and the height adjusting bracket 6 d is drawn from and out the frame by stages, so that the height control of the arm seat 6 a or the height and length control thereof can be simultaneously performed according to the physical or environment conditions of the sitter. Also, other end of the frame 6 b is fixed to the bracket 7 located on the lower surface of the seat 2, not the thoracic support 4. Besides this construction, since it is the same as the first embodiment of the present invention, further description is omitted here.

Also, in the chair 1 a with separate and interconnecting type lumbar and thoracic supports according to another embodiment of the present invention, excepting that the armrest 6 is not interconnected to the thoracic support 4, since the operation thereof is the same as the first embodiment of the present invention, further description on this is omitted here.

Although several exemplary embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 

1. A chair with separate and interconnecting type lumbar and thoracic supports having a back support divided into a lumbar support and a thoracic support with a frame, a seat integrally formed on the lumbar support through an embedded frame, the frame of the thoracic support elastically and tiltably connected to another frame or a bracket located at a lower surface of the seat, and an armrest, wherein the embedded frame is divided into a main frame extending from the seat to a lower half portion of the lumbar support and at least one auxiliary frame located on an upper half portion of the lumbar support and a plate spring is attached backward over the main frame and the auxiliary frame, which are separated from each other.
 2. The chair with separate and interconnecting type lumbar and thoracic supports as recited in claim 1, wherein the thoracic support comprises a short edge for contacting with an upper end portion of the lumbar support and an extending portion formed via the short edge.
 3. The chair with separate and interconnecting type lumbar and thoracic supports as recited in claim 1, wherein one end of a frame of the armrest is fixed to a lower portion of an extending portion of the thoracic support through a fixing means, thereby the armrest is lifted by interlocking with the thoracic support during a backward tilting of the thoracic support.
 4. The chair with separate and interconnecting type lumbar and thoracic supports as recited in claim 1, wherein the armrest comprises a height adjusting bracket having a plurality of fixing protrusions therein connected to the arm seat and a frame having one end portion thereof inserted into the height adjusting bracket and a plurality of grooves for inserting the fixing protrusions therein formed at said one end portion of the frame, and the height adjusting bracket is drawn from and out the frame by stages, thereby a height control of the arm seat or height and length control thereof can be simultaneously performed.
 5. The chair with separate and interconnecting type lumbar and thoracic supports as recited in claim 1, wherein the thoracic support comprises a body, which is consist of a cushion material and a soft outer cover covering an outer surface of the cushion material, again the frame is fixed to a back surface of the body, a hard outer cover is covered and overlaid on a back surface of the frame, and a cutting portion is transversely formed at a position in that an extending portion of the hard outer cover is formed, whereby a bending stress can be released during backward tilting of the thoracic support.
 6. The chair with separate and interconnecting type lumbar and thoracic supports as recited in claim 1, wherein at least one air entrance cap having a plurality of air inflow and outflow holes is formed at the side surface of the seat.
 7. The chair with separate and interconnecting type lumbar and thoracic supports as recited in claim 1, one end of a connecting frame is connected to a lower end portion of the frame of the thoracic support, other end of the connecting frame is inserted into and fixed to a pivotable frame of the bracket, which is pivotally mounted on the bracket fixed to a lower surface of the seat, by means of a link for controlling the length thereof, and the pivotable frame is elastically supported by a plate spring.
 8. The chair with separate and interconnecting type lumbar and thoracic supports as recited in claim 3, wherein the armrest comprises a height adjusting bracket having a plurality of fixing protrusions therein connected to the arm seat and a frame having one end portion thereof inserted into the height adjusting bracket and a plurality of grooves for inserting the fixing protrusions therein formed at said one end portion of the frame, and the height adjusting bracket is drawn from and out the frame by stages, thereby a height control of the arm seat or height and length control thereof can be simultaneously performed.
 9. The chair with separate and interconnecting type lumbar and thoracic supports as recited in claim 2, one end of a connecting frame is connected to a lower end portion of the frame of the thoracic support, other end of the connecting frame is inserted into and fixed to a pivotable frame of the bracket, which is pivotally mounted on the bracket fixed to a lower surface of the seat, by means of a link for controlling the length thereof, and the pivotable frame is elastically supported by a plate spring.
 10. The chair with separate and interconnecting type lumbar and thoracic supports as recited in claim 3, one end of a connecting frame is connected to a lower end portion of the frame of the thoracic support, other end of the connecting frame is inserted into and fixed to a pivotable frame of the bracket, which is pivotally mounted on the bracket fixed to a lower surface of the seat, by means of a link for controlling the length thereof, and the pivotable frame is elastically supported by a plate spring. 